and the sun stops shining at night. In contrast, power generated from coal and natural gas is consistent, and able to be ramped up and down quickly to meet demand.

This presents a conundrum for clean energy advocates. How do you make renewable energy not only cheap enough, but reliable enough, to compete with fossil fuels?

The answer may lie in the types of energy storage used to capture the power generated from these renewable sources. Better batteries could make it possible for utility companies to leverage renewable energy sources at scale as primary power sources, rather than as clean backups to traditional dirty fuels.

Powering the Grid

The power grids that charge and recharge modern life are complicated beasts, comprised of many different companies and technologies that make it possible to generate power, then route that power to homes and businesses.

These grids operate on a basic principle: once energy is generated, it is sent out for consumption. If it is not being consumed immediately, it needs to be stored in some fashion so it can be released back into the grid when end users are ready to consume it.

It sounds easy in theory, but it quickly gets complicated in practice.

When businesses and homes need power, they typically need it immediately. This means demand for grid power can fluctuate a lot, and it can fluctuate quickly. Power supply must match demand as adequately as possible, on time and on budget. Failure to meet demand sufficiently and on time results in power failures or blackouts. Failure to meet demand on-budget means a power provider eventually goes out of business.

This is where the benefits of fossil
fuels become evident. Fossil fuel-pow-
ered energy plants generate consis-
tent power, since humans, not nature,
control their fuel sources, and the
different fossil fuel power generation
technologies (such as coal, oil, and
natural gas) can be scaled up or down
to meet demand fluctuations. Despite
being dirty (basically, the fuels are
burned to heat water to turn turbines
that generate electricity, releasing car-
bon dioxide and other contaminants
into the atmosphere in the process),
they are (at the moment) reliable.

Renewable energy sources, on the other hand, are clean and their fuel is free and abundant. However, the power generated by water, wind, and solar sources must be stored somewhere after it is generated, since it is intermittent.

The top method utilized in the U.S. for renewable energy storage is pumped-storage hydroelectric, which provides 95% of grid-scale electricity storage in the country, according to the U.S. Department of Energy. Pumped-storage hydro utilizes multiple reservoirs to store and release electricity in a highly efficient and responsive manner, allowing power grids to react quickly to fluctuations in demand.

According to electric power holding company Duke Energy, “ Pumped-storage hydro plants store and generate energy by moving water between two reservoirs at different elevations.” When demand is low, “Excess energy is used to pump water to an upper reservoir.” When there’s high demand, the water is released from the upper reservoir to generate power.

However, building these storage systems requires massive time and resource investments, and the location of these storage systems is highly dependent on geography.

This is where battery technology
comes in. On the grid, the right bat-
tery technology may be able to store
and release energy at far less cost than
pumped-storage hydro. Some battery
developments are also enabling the
transition to electric vehicles, further
reducing reliance on non-renewable
fossil fuels.

One of the main battery types currently used for energy storage is the lithium-ion battery. Lithium-ion batteries power the handheld tech gadgets we use every day, including smartphones. They also provide energy storage for electric cars, and extremely large lithium-ion batteries are increasingly being used in power grids to store energy from renewable sources.

Lithium-ion batteries are inexpensive and energy-dense compared to batteries made with other materials. They also degrade relatively slowly, losing just a fraction of their power after each use.

“Over the past decade, we have seen a tremendous cost reduction of lithium-ion battery technology, by approximately 10 times,” says William

Chueh, an assistant professor of Mate-
rials Science and Engineering at Stan-
ford University working on renewable
energy storage technologies. “This
has been responsible for the boom in
electric vehicles and for storing inter-
mittent solar and wind electricity.”
However, lithium-ion batteries
have one big problem: they still are
not priced competitively enough to be
used at scale on grids to store energy
from renewable sources.
“To realize a complete penetration
of batteries for storing intermittent
renewable electricity, the cost needs
to decrease by another order of mag-
nitude, and the scalability needs to be
greatly improved,” says Chueh.
Those developments are unlike-
ly, says Ben Schiltz, head of Energy
Storage Communications at the U.S.
Department of Energy’s Argonne Na-
tional Laboratory, which has multiple
energy storage research projects in
progress.
“Today, the industry continues to
make incremental improvements to
lithium-ion batteries. However, we
are reaching the theoretical limit of
what can be done with these batter-
ies,” Schiltz says. “Developing safe
“Incumbent
technologies
are still on a steep
cost-down curve,
which is challenging
for new technologies
to compete with,” says

Stanford University’s
William Chueh.